The present invention relates to a thermal printer for printing an image or characters on a print paper by transferring thereto the ink coated on an inked ribbon or an inked film by means of a selectively heated thermal head, and more particularly, to a thermal printer suitable for the printing operation on papers of a rough surface to obtain a high printing quality.
A thermal printer is classified into two types, i.e., a serial printer and a line printer. The serial thermal printer as disclosed in the U.S. Pat. No. 3,855,448 comprises a platen extending in the lateral direction to support a print paper, a thermal head having a plurality of heater elements arrayed in the vertical direction and mounted on a carrier unit to move in parallel with the platen, and an inked ribbon provided on the carrier unit so as to be located between the print paper on the platen and the actuating surface of the thermal head on which the heater elements are provided. The printing operation in a print line is carried out by the selective actuation of the heater elements and lateral movement of the carrier unit. The print paper is fed by one print line after the printing operation is completed in the print line.
A line thermal printer is disclosed in the U.S. patent application Ser. No. 736,889, filed on May 22, 1985, entitled "PRINT PAPER AND INKED FILM FEEDING MECHANISM FOR A THERMAL PRINTER" and assigned to the present assignee. It comprises a platen extending in the lateral direction, a thermal head having a width sufficient to cover the print line length of a print paper and a plurality of heater elements arrayed over the entire width of the thermal head, and an inked film having a width substantially equal to the print line length of the print paper. The print paper and the inked film are movable together and fed into the space between the thermal head and the platen. The printing operation is carried out by the selective actuation of the heater elements and the line feed of the print paper and the inked film.
In either type of the thermal printers, the ink coated on the inked ribbon or film is thermally transferred to the surface of the print paper according to the image or characters to be printed. The heater elements of the thermal head is actuated with the same amount of power and the thermal head is pressed onto the print paper with the same amount of force regardless of the surface quality of the print paper. Where the print paper has a rough surface, however, the ink is difficult to adhere to the minute concaves of the rough surface of the paper. Accordingly, the good printing quality cannot be obtained on the rough surface paper such as the bond paper, with the result that only papers if excellent quality having the smooth surface are used for the thermal printer.
Further, in the conventional thermal printer, the image and characters formed by the thermally transferred ink having undesirable luster due to insufficient permeation of the ink into the print paper.